How to Build an Outdoor Fireplace

Outdoor fireplaces are a great way to enjoy the backyard at night, even when the weather is chilly. This is a project for a determined do-it-yourselfer with prior masonry experience though the availability of preformed hearths and chimney flues simplifies the process considerably.

Getting Started

Start by checking out ordinances, picking a building spot, and gathering all the necessary materials.

Ordinances, Codes, and Regulations

First of all, do your homework. Check with the city to find out what ordinances and codes are in place that might affect you. Ask what permits will be required and how much they will cost. It is also a good idea to check with your insurance agent to see if the fireplace will change your home insurance premiums. Knowing what to expect can save you a lot of money, stress, and frustration later on.

Where to Build

Next, pick a spot to build the fireplace. It needs to be a safe distance from your home and any other outbuildings, such as a detached garage, barn, or shed. It's also important that there are no overhanging branches or other combustible vegetation nearby.

Materials

In addition to the tools and supplies listed below, use the printable plans to the right to help guide you in the process. They can be viewed and printed using Adobe Reader. The exact amount of materials and supplies needed will depend on your personal preferences and modification of the basic plans.

Step-by-Step Process

There are many ways to design and customize an outdoor fireplace, but the following process covers the basic steps that are involved. Modify as needed depending on your specific design.

Lay the Foundation

It's possible to build a fireplace on top of an existing concrete or stone patio, but otherwise you'll have to start the foundation with a concrete pad to support the weight of the structure.

Excavate a flat rectangular area of the existing soil about 10 percent larger than the footprint of the planned fireplace until firm subsoil is reached. Typical sizing may be 3 x 4 feet or 4 x 6 feet and subsoil is usually at a depth of four to six inches.

Compact the base of the excavated area with a tamper and spread about two inches of gravel in the bottom for drainage

Build a rectangular frame with 2 x 6s in the size and shape of the fireplace foundation and set it on top of the gravel. Adjust the grade of the gravel as needed to make the frame level.

Cut support stakes out of 2 x 4s (with one pointed end) and drive these into the ground in several places along the edge of the frame to prevent the 2 x 6s from bowing out under the pressure of the concrete.

Fill the frame with concrete and allow it to set for 24 hours before proceeding.

Build the Base

The fireplace will sit on a cinder block pedestal on top of the foundation. These are usually the height of two or three cinder blocks and are often three-sided to allow access to store firewood on one side, but you can build it according to your own design using these steps.

Spread a one-inch thick layer of mortar in an eight-inch wide strip around the perimeter of the concrete pad and place the first course of cinder block on top, spreading a 1/2-inch layer of mortar in the vertical joints between each one. Make sure that each block is plumb, level, and square as you go.

Spread a 1/2-inch layer of mortar over the top of the first course of cinder blocks and install the second course. This course should be offset from the first so that each cinder block straddles the joint between the two under it. You'll have to cut the last block in this course in half to make it comes flush with end of the first course.

Continue laying cinder blocks until the desired height is reached.

Spread a half inch thick layer of mortar on the top of the last course and install the hearth block on top of the cinder block pedestal.

Hearth Walls and Chimney Cap

The fire will sit on the hearth block and the three-sided hearth wall structure will contain the flames. The footprint of the walls can be the same as the pedestal or you can bring them in slightly to create a ledge on the outside of the hearth walls. Three or four feet is the typical height, but you can adjust based on your own preferences. The hearth walls will support the chimney cap.

Build the hearth walls with the cinder blocks in the same manner as the pedestal was constructed.

Once the mortar has cured for at least 24 hours, mortar a base of fireplace brick on top of the hearth block using refractory (heat resistant mortar).

Mortar fireplace bricks into place on the interior of the three hearth walls using 3/8-inch joints of refractory mortar.

Spread a half-inch thick layer of mortar on top of the last course of the hearth walls and install the chimney cap.

At this point you can consider trimming the exterior as well. For example, you may want to install an arched opening for the hearth, which will require building a wooden frame to support it.

The materials chosen for the exterior finishing will determine the installation technique - follow the manufacturers' specifications.

Styles and Options to Consider

Outdoor fireplaces come in a variety of looks and designs and can be wood burning or gas. If you choose to go with gas, hire a professional contractor for this part. They can install the gas lines and logs in the fireplace once you've built the structure. There are also outdoor fireplace kits that simplify the process of building one and make it easy to achieve a particular style.

Enjoy Your Outdoor Room

Knowing how to build an outdoor fireplace is only the first step. Once you have the fireplace built, you can begin to decorate and enjoy your new outdoor room. Consider adding solar deck lighting, strategically placed for ambiance. Another option to is to create an entire outdoor kitchen. These projects will not only bring you years of outdoor fun, but will add value to your home.

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